1. Field of the Invention
The present invention relates to trip mechanisms for earth working tools such as moldboard plows.
2. Prior Art
A wide variety of trip beam plows have been used in the prior art. My U.S. Pat. No. 3,550,690 illustrates one type of trip beam linkage. In addition, early patents show various pivoting lever trip linkages, for example, Australian Pat. No. 107,929, and U.S. Pat. No. 837,335. Devices using slide members tend to wear because of the high loads involved. A trip beam which operates from a single pivot axis is desired because of simplicity, but the device must provide a high clearance tripping action without overstressing any parts.
A pivoting linkage utilizing a single pivot for the earth working tool and compression springs for automatic reset has been made and sold by others. Such a device requires large compression springs, and is not capable of providing the desired tripping clearance, or holding and reset force. Also, costs are high, particularly the cost of the heavy compression springs used.
It has long been recognized that the use of tension springs for controlling loads is desirable, but again, when using the type of folding linkages mentioned, tension springs have heretofore not been used because of problems with trip geometry, space considerations and similar factors.